DescriptionDigital image of Hudson & Manhattan R.R. postcard titled: At work in the air-lock. 1908. Courtesy of Leon Yost. A view of seven men, none identified, working outside the airlock. The front of postcard has holographic ink note "April 3, This was before it is completed." Postmarked April 3, 1908. From a series: The Hudson and Manhattan Railroad Company Tunnel (McAdoo system) under the Hudson River.